Phtopigments undergo chemical alterations when

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Unformatted text preview: = low light and grey scale Cones = color vision 3 parts: Outer segments- detect light stimuli Inner segment- contains metabolic machinery of cell. Synaptic terminal- transmits signal generated in photoreceptors on light stimulation to next cells in visual pathway. • • • • • Phtopigments- undergo chemical alterations when activated by light consists of two compartments Opsin- protein that is integral part of the disc membrane Retinene-derivative of vitamin A Light absorbing part of photopigment • • • • • • • • • • • • • • • • • • • • • • Four different pigments Rod pigment- provide vision only in shades of gray Rhodopsin- absorbs all visible wavelengths Cone pigments Respond selectively to various wavelengths of light Make color vision possible Photoreceptors release glutamate onto Bipolar cells in the dark The receptor release glutamate onto a bipolar cell in the dark Some bipolar cells are hyperpolarized by NT- NT closes cation channel. Some bipolar cells are depolarized by NT- NT opens cation channel Photoreceptors decrease glutamate release onto bipolar cells in the light So in light, receptors hyperpolarize and reduce glutamate NT release. Some bipolars depolarize On biopolars DBC (depolarizing bipolar cells) Some hyperpolarize Off bipolars HBC (hyper bipolarizing cells) Cones sensitive to different wavelengths Each cone expresses a photopigment with a unique absorbance spectrum On ganglion cells depolarize in the light Off ganglion cells hyperpolarize in the light. • • • As any as 100 photoreceptors may converge onto a bipolar cell Several bipolars converge onto a single ganglion cells. Rods: more numerous in the periphery, high sensitivity, night vision, low acuity, much convergence in retinal pathway, vision in shades of gray. • Cones: concentrated in fovea, low sensitivity, day vision, high acuity, little convergence in retinal pathways, color vision. • • The receptive field in ganglion cell is a circle of photoreceptors in the retina. A ganglion cell ma...
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This note was uploaded on 09/23/2010 for the course NPB 8746546 taught by Professor Goldberg during the Spring '10 term at UC Davis.

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